Network Working Group D. Eastlake
Request for Comments: 2606 A. Panitz
BCP: 32 June 1999
Category: Best Current Practice
Reserved Top Level DNS Names
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
To reduce the likelihood of conflict and confusion, a few top level
domain names are reserved for use in private testing, as examples in
documentation, and the like. In addition, a few second level domain
names reserved for use as examples are documented.
Table of Contents
1. Introduction............................................1
2. TLDs for Testing, & Documentation Examples..............2
3. Reserved Example Second Level Domain Names..............2
4. IANA Considerations.....................................3
5. Security Considerations.................................3
References.................................................3
Authors' Addresses.........................................4
Full Copyright Statement...................................5
1. Introduction
The global Internet Domain Name System is documented in [RFC 1034,
1035, 1591] and numerous additional Requests for Comment. It defines
a tree of names starting with root, ".", immediately below which are
top level domain names such as ".com" and ".us". Below top level
domain names there are normally additional levels of names.
Eastlake & Panitz Best Current Practice [Page 1]RFC 2606 Reserved Top Level DNS Names June 19992. TLDs for Testing, & Documentation Examples
There is a need for top level domain (TLD) names that can be used for
creating names which, without fear of conflicts with current or
future actual TLD names in the global DNS, can be used for private
testing of existing DNS related code, examples in documentation, DNS
related experimentation, invalid DNS names, or other similar uses.
For example, without guidance, a site might set up some local
additional unused top level domains for testing of its local DNS code
and configuration. Later, these TLDs might come into actual use on
the global Internet. As a result, local attempts to reference the
real data in these zones could be thwarted by the local test
versions. Or test or example code might be written that accesses a
TLD that is in use with the thought that the test code would only be
run in a restricted testbed net or the example never actually run.
Later, the test code could escape from the testbed or the example be
actually coded and run on the Internet. Depending on the nature of
the test or example, it might be best for it to be referencing a TLD
permanently reserved for such purposes.
To safely satisfy these needs, four domain names are reserved as
listed and described below.
.test
.example
.invalid
.localhost
".test" is recommended for use in testing of current or new DNS
related code.
".example" is recommended for use in documentation or as examples.
".invalid" is intended for use in online construction of domain
names that are sure to be invalid and which it is obvious at a
glance are invalid.
The ".localhost" TLD has traditionally been statically defined in
host DNS implementations as having an A record pointing to the
loop back IP address and is reserved for such use. Any other use
would conflict with widely deployed code which assumes this use.
3. Reserved Example Second Level Domain Names
The Internet Assigned Numbers Authority (IANA) also currently has the
following second level domain names reserved which can be used as
examples.
Eastlake & Panitz Best Current Practice [Page 2]RFC 2606 Reserved Top Level DNS Names June 1999
example.com
example.net
example.org
4. IANA Considerations
IANA has agreed to the four top level domain name reservations
specified in this document and will reserve them for the uses
indicated.
5. Security Considerations
Confusion and conflict can be caused by the use of a current or
future top level domain name in experimentation or testing, as an
example in documentation, to indicate invalid names, or as a synonym
for the loop back address. Test and experimental software can escape
and end up being run against the global operational DNS. Even
examples used "only" in documentation can end up being coded and
released or cause conflicts due to later real use and the possible